Casual Friday — the H-II Transfer Vehicle (HTV)

The H-II Transfer Vehicle (HTV), developed and built in Japan, is an unmanned cargo transfer spacecraft made to deliver supplies to the International Space Station (ISS). The first HTV was launched a week ago, and arrived at ISS in the early hours of the morning today (Japan time). Now it’s up to the ISS crew to unload the supplies the HTV carries, and reload it with trash for its eventual destructive plunge into the atmosphere over the Pacific Ocean.

Just as was the case for this maiden trip, future HTVs will also be launched from the Tanegashima Space Center aboard an H-IIB launch vehicle with up to 6,000 kg of supplies. After some on-orbit checkout time, the HTV approaches close to the ISS, and the Space Station Remote Manipulator System (SSRMS, a.k.a. ‘Canadarm2’) is used to grapple the HTV and berth it to the ISS. Once the HTV’s supplies are unloaded and it’s packed full of trash, the HTV separates from the ISS and reenter the atmosphere.

With the shuttle nearing retirement, HTV flights will play a big role in supplying the ISS with the equipment needed to keep it running in tip-top shape. While it’s certainly not the only means of getting cargo to the station, the HTV does have some unique capabilities. Once the shuttle retires, it’ll be the only way to get large, unpressurized cargo to ISS for some time. This is particularly important for bulky things that just won’t fit through airlock doors. Even for pressurized cargo (lab equipment and the like), HTV benefits from the fact that it gets berthed to ISS rather than being docked — the berthing hatches are considerably larger than any existing docking port, handy for bulky items destined for spots inside the ISS modules.

The H-II Transfer Vehicle (HTV), built and developed in Japan, is an unmanned cargo transfer spacecraft made to deliver supplies to the International Space Station (ISS). Here’s a JAXA animation showing a typical HTV mission…